CN116068005A - A method for evaluating TOC of source rocks using T1-T2 two-dimensional nuclear magnetic resonance - Google Patents

Abstract

The invention provides a method for utilizing T ₁ ‑T ₂ Method for evaluating TOC of hydrocarbon source rock by two-dimensional nuclear magnetic resonance by obtaining high-quality T ₁ ‑T ₂ Spectral signal, then build T ₁ ‑T ₂ Percentage S of signal area characterizing TOC on spectrum _TOC The relation model with the measured total organic carbon content TOC is used for calculating the total organic carbon content TOC of the hydrocarbon source rock to be measured, overcoming uncertainty and quantitative inaccuracy of the TOC content representation of the hydrocarbon source rock caused by different instrument parameters and different measurement parameters, realizing the evaluation of the characteristics of the hydrocarbon source rock while evaluating the oil content and the water content of a hydrocarbon source rock reservoir, and filling up the process of T ₁ ‑T ₂ The TOC spectral evaluation method has the advantages of simple operation, high accuracy and wide application range and prospect.

Description

A method for evaluating TOC of source rocks using T1-T2 two-dimensional nuclear magnetic resonance

technical field

The invention relates to the technical field of nuclear magnetic resonance evaluation of oil and gas engineering, and particularly designs a method for evaluating TOC of source rocks by using T ₁ -T ₂ two-dimensional nuclear magnetic resonance.

Background technique

The T ₁ -T ₂ two-dimensional nuclear magnetic resonance of source rocks can identify multiple pore fluid components through one analysis, and has become a hot technology in the evaluation of source rock oil and gas reservoirs. However, the measurement of T ₁ -T ₂ is limited by instruments, Due to the influence of multiple factors such as samples and operations, the spectral effect and interpretation results are quite different.

Instrument and operation factors include magnetic field strength, echo interval, probe diameter, measurement parameters, inversion algorithm, etc.; sample factors include storage tightness, temperature and analysis timeliness, etc. Due to many influencing factors, the number of T ₁ -T ₂ signal peaks varies greatly, ranging from one to five or six peaks, and fluid signals and noise signals coexist, making identification and verification of signal peaks difficult.

For the T ₁ -T ₂ spectra of source rock oil reservoirs, there are five main types of hydrocarbon signals to be interpreted: (1) kerogen/solid bitumen, adsorbed oil, and mobile oil (Jinbu Li, 2020); (2) Kerogen or organic matter, methane (Marc Fleury, 2016; HanJiang, 2019; Xinhua Ma, 2020); (3) high-viscosity hydrocarbons, immovable oil, movable oil (Andrew C. Johnson, 2021); (4) cheese Roots (invisible by low-field NMR), bitumen (partially visible), oil in organic pores (movable, immovable), oil in inorganic pores (Ravinath Kausik, 2015); (5) kerogen, oil/bitumen ( Mohammad Sadegh Zamiri, 2021). It can be seen that the understanding of kerogen, bitumen, organic matter, and oil in organic pores is relatively confusing, and it is mainly qualitative, and the quantitative evaluation of total organic carbon (TOC) has not been realized.

Contents of the invention

In order to solve the above-mentioned problems in the prior art, the present invention is proposed. The purpose is to overcome the uncertainty of the current source rock reservoir multi-component information T ₁ -T ₂ two-dimensional nuclear magnetic resonance measurement and interpretation, to achieve high-precision quantitative calculation of TOC content, and provide a basis for the TOC of source rock oil and gas reservoirs. Evaluation provides reliable technical support.

The present invention proposes a method for evaluating source rock TOC by using _T1 - _T2 two-dimensional nuclear magnetic resonance, comprising the following steps:

Step 1: Establish a relationship model between the signal area percentage S _TOC representing TOC on the T ₁ -T ₂ spectrum of the source rock and the measured total organic carbon content TOC of the corresponding source rock;

Step 2: Perform T ₁ -T ₂ two-dimensional nuclear magnetic resonance analysis on the source rock to be tested to obtain the T ₁ -T ₂ spectrum of the source rock to be tested;

Step 3: Calculate the TOC of the source rock to be tested based on the relationship model obtained in Step 1.

As a specific embodiment of the present invention, the step 1 includes:

Step 11: Perform T ₁ -T ₂ two-dimensional nuclear magnetic resonance analysis on the source rock to obtain the T ₁ -T ₂ spectrum of the source rock;

Step 12: Use the rock pyrolysis method to actually measure the total organic carbon content of the source rock, and obtain the measured total organic carbon content TOC of the corresponding source rock;

Step 13: Based on the T ₁ -T ₂ spectrum of the source rock obtained in step 11 and the measured total organic carbon content TOC of the corresponding source rock obtained in step 12, obtain the T ₁ -T ₂ spectrum characterization of the source rock The relationship model between the signal area percentage S _TOC of TOC and the measured total organic carbon content TOC of the corresponding source rock.

As a specific embodiment of the present invention, in step 11 and/or step 2, the T ₁ -T ₂ two-dimensional nuclear magnetic resonance analysis parameters are: the magnetic field strength is 20±5Mhz, the probe diameter is not less than 15mm, and the pulse sequence is inversion The recovery method IR-CPMG, the echo interval TE is 0.06ms, the waiting time TW is 10ms, and the inversion method is the regularization method.

As a specific embodiment of the present invention, the signal-to-noise ratio of the T ₁ -T ₂ spectrum measured in step 11 and/or step 2 is SNR>1000, and the number of signal peaks is not less than 3.

It should be noted that the signal-to-noise ratio of the T ₁ -T ₂ spectrum measured above is SNR>1000, and the signal-to-noise ratio is high, so that the noise signal can be suppressed, and high-quality, high-resolution, or high-resolution T ₁ -T ₂ spectrum, which is the prerequisite and key factor for later modeling and calculation of TOC.

As a specific embodiment of the present invention, in the step 13, the following steps are also included:

Step 13a: Calculate or read the T ₁ -T ₂ spectral signal area A _TOC ,

Step 13b: Calculate or read the total effective area ΣA _i of the T ₁ -T ₂ spectrum,

Step 13c: Calculate A _TOC as a percentage of ΣA _i S _TOC :

S _TOC ＝(A _TOC /∑A _i )×100％ Formula 1

Step 13d: Establish a relationship model between S _TOC and TOC through linear regression:

TOC＝a×S _TOC +b Formula 2

In the formula, a and b are the regression coefficients, where a is the slope of the regression line; b is the intercept of the regression line.

As a specific embodiment of the present invention, in the step 13a, signal overlap cannot calculate or read the T ₁ -T ₂ spectrum signal area, and the signals need to be separated before the later modeling calculation can be performed. Therefore, if the signals overlap, By adjusting the isoline of the T ₁ -T ₂ two-dimensional spectrum or looking for the lowest value between the signal peaks in the spectrum data table as the split point.

As a specific implementation manner of the present invention, in the step 13b, the effective area does not include noise signals.

As a specific embodiment of the present invention, the value range of T ₁ is [15,500]; the value range of T ₁ /T ₂ is [30,600].

Compared with prior art, the beneficial effect of the present invention is:

1. The present invention obtains high-quality T ₁ -T ₂ spectrum signals, and establishes a relationship model between the signal area ratio S _TOC and the measured total organic carbon content TOC on the T ₁ -T ₂ spectrum, thereby calculating The total organic carbon content TOC of the source rock to be measured, compared with the prior art, the present invention overcomes the uncertainty and quantitative inaccuracy in the TOC content characterization of the source rock caused by different instrument parameters and different measurement parameters, and realizes While evaluating the oiliness and water content of source rock reservoirs, the evaluation of source rock characteristics fills the gap in evaluating TOC by T ₁ -T ₂ spectrum. It is easy to operate, high in accuracy, and has a wide range of applications and prospects.

2. The present invention can finely identify the source rock reservoir pore fluid type and occurrence state through T ₁ -T ₂ two-dimensional nuclear magnetic resonance, and at the same time evaluate the TOC content without processing samples or adding new technical means, It has the characteristics of measurement economy and accurate evaluation.

Description of drawings

Fig. 1 is the nuclear magnetic resonance _T1 - _T2 spectrogram of the sample Wooh-1 in the embodiment 1 of the present invention;

Fig. 2 is the nuclear magnetic resonance T ₁ -T ₂ spectrogram of the sample Wooh-2 in Example 2 of the present invention;

Fig. 3 is the linear regression modeling data figure of sample Wooh-1, sample Wooh-2 in the embodiment 1～2 of the present invention;

Fig. 4 is the sample nuclear magnetic resonance T ₁ -T ₂ spectrogram in comparative example 1;

Fig. 5 is the sample nuclear magnetic resonance T ₁ -T ₂ spectrogram in comparative example 2;

Fig. 6 is the sample nuclear magnetic resonance T ₁ -T ₂ spectrogram in comparative example 3;

Fig. 7 is the NMR T ₁ -T ₂ spectrogram obtained in Example 3 of the present invention;

Fig. 8 is a graph of linear regression modeling data obtained in Example 3 of the present invention.

Among them, 1-kerogen signal; 2-adsorbed oil signal; 3-moveable oil signal; 4-structure water signal; 5-moveable water signal; 6-adsorbed water signal; 7-kerogen signal; 8-moveable Oil signal; 9-structure water signal; 10-pore water signal; 11-fracture water signal; 12-kerogen signal; 13-hydroxide signal; 14-methane signal in porous media; 15-water (clay, granular between) signals.

Detailed ways

In order to make the present invention easier to understand, the present invention will be described in detail below in conjunction with the embodiments and the accompanying drawings, and these embodiments are for illustrative purposes only, and do not limit the scope of application of the present invention.

The nuclear magnetic resonance instrument used in each embodiment of the present invention is MesoMR23-040V, adopts SR-CPMG pulse sequence to carry out measurement, adopts instrument's own data collection software to carry out data collection.

Example 1

This example provides a method for evaluating the TOC of source rocks using T ₁ -T ₂ two-dimensional nuclear magnetic resonance. This method is used to test the shale core of Well W. Well W is a shale oil well. During the core selection process, the The target section of the well was drilled and cored by pressure-holding drilling, and the core was frozen with liquid nitrogen. The core number was Wooh-1, and the lithology was fine silt-bearing mudstone. The details are as follows:

Step 1: The T ₁ -T ₂ spectrum measured by Wooh-1 at a resonance frequency of 19MHz, a probe coil diameter of 25mm, a callback interval TE of 0.06ms, and a waiting time TW of 10ms is shown in Figure 1;

It can be seen from Figure 1 that the T ₁ -T ₂ spectrum of the Wooh-1 sample has a high signal-to-noise ratio and good separation. Among them, the T ₁ -T ₂ spectrum of Wooh-1 has 5 signal peaks, and the signal of TOC is very weak , are barely visible.

Step 2: Calculate or read the total effective area ∑A _i of the T ₁ -T ₂ spectrum of Wooh-1, and calculate the percentage S _TOC of A _TOC in ∑A _i :

S _TOC = (A _TOC /∑A _i ) × 100% = 0.85%;

Step 3: Establish the relationship model between S _TOC and TOC, as shown in Figure 3, calculate the TOC of Wooh-1 by modeling formula 2:

TOC=a×S _TOC +b=1.02%

Analysis of the data obtained in Example 1: It is not difficult to see from Figure 3 that the _STOC and TOC data points of the Wooh-1 sample are located on both sides of the modeling regression line and concentrated, which is highly representative.

Two pieces of shale Wooh-1 in Example 1 were subjected to rock pyrolysis measurement, and the obtained TOC results were 0.82%, as shown in FIG. 3 .

The absolute error between the calculated TOC and the measured TOC of the sample Wooh-1 in this embodiment is 0.20%, and the data is valid and reliable.

Example 2

This example provides a method for evaluating the TOC of source rocks using T ₁ -T ₂ two-dimensional nuclear magnetic resonance. This method is used to test the shale core of Well W. Well W is a shale oil well. During the core selection process, the The target section of the well was drilled and cored by pressure-holding drilling, and the core was frozen with liquid nitrogen. The core number is Wooh-2, and the lithology is silt-bearing mudstone and bioclastic fine powder crystal dolomite. The details are as follows:

Step 1: The T 1 _{-T 2} spectrum measured by Wooh-2 at a resonance frequency of 19MHz, a probe coil diameter of 25mm, a callback interval TE of 0.06ms, and a waiting time TW of 10ms, as shown in Figure 2;

It can be seen from Figure 2 that the T ₁ -T ₂ spectrum of the Wooh-2 sample has a high signal-to-noise ratio and good separation. The T ₁ -T ₂ spectrum of Wooh-2 has 4 signal peaks, and the TOC signal is relatively strong.

Step 2: Calculate or read the total effective area ∑A _i of the T ₁ -T ₂ spectrum of Wooh-2, and calculate the percentage S _TOC of A _TOC in ∑A _i :

S _TOC ＝(A _TOC /∑A _i )×100%＝6.36%

Step 3: Establish the relationship model between S _TOC and TOC, as shown in Figure 4, calculate the TOC of Wooh-2 by modeling formula 2:

TOC=a×S _TOC +b=2.47%

Analysis of the data obtained in Example 2: It is not difficult to see from Figure 3 that the _STOC and TOC data points of the sample Wooh-2 are located on both sides of the modeling regression line and concentrated, which is relatively representative.

The sample Wooh-2 of Example 2 was subjected to rock pyrolysis measurement, and the obtained TOC results were 2.63%, as shown in Figure 3.

The absolute error between the calculated TOC and the measured TOC of the sample Wooh-2 in this embodiment is 0.16%.

The average absolute error between the TOC results obtained in Examples 1 and 2 and the actual measurement is 0.18%. In Figure 3, the S _TOC and TOC data points of samples Wooh-1 and Wooh-2 are respectively located on both sides and both ends of the modeling regression line , the representativeness is strong, indicating that the evaluation method provided by the present invention is reliable.

Comparative example 1

In this comparative example, sample D-1 is used, the lithology is shale, and the T ₁ -T ₂ spectrum obtained by nuclear magnetic resonance with a magnetic field strength of 21.36 MHz is shown in Figure 4. The signal analysis is as follows:

The nuclear magnetic resonance test sample D-1 with a magnetic field strength of 21.36MHz is used, and the obtained hydrocarbon signals include kerogen 1, adsorbed oil 2, and movable oil 3; water signals include structural water 4, movable water 5, and adsorbed water 6 ; It can be seen from Figure 4 that the various signals of the T ₁ -T ₂ spectrum obtained by sample D-1 all have peak shapes superimposed on each other,

Comparative example 2

In this comparative example, sample D-2 is used, the lithology is shale, and the T1 _{- T2} spectrum obtained by NMR with a magnetic field strength of 12 MHz is shown in Figure 5. The signal analysis is as follows:

The nuclear magnetic resonance test sample D-2 with a magnetic field strength of 12MHz is used, and the obtained hydrocarbon signals include kerogen signal 7 and movable oil signal 8; water signals include structural water signal 9, pore water signal 10, and fracture water signal 11; It can be seen from Fig. 5 that the T ₁ -T ₂ spectrum obtained from sample D-2 has peak shapes of kerogen signal 7 and water signal 9 superimposed, and the position of kerogen signal 7 is comparable to that in Fig. 4 of Comparative Example 1.

Comparative example 3

In this comparative example, sample D-3 is used, the lithology is shale, and the _T1 - _T2 spectrum obtained by nuclear magnetic resonance with a magnetic field strength of 23.7MHz is shown in Figure 6. The signal analysis is as follows:

The nuclear magnetic resonance test sample D-3 with a magnetic field strength of 23.7MHz is used, and the hydrocarbon signals in the obtained T ₁ -T ₂ spectrum include kerogen signal 12 and methane signal 14 in the porous medium, 13 is the hydroxide signal, 15 is the water (clay, intergranular) signal; it can be seen from Figure 6 that the T ₁ -T ₂ spectrum obtained from sample D-3 has the peak shape superposition of kerogen signal 12 and hydroxide signal 13; kerogen signal 12 There are differences in the direction of the major axis of , and Fig. 4 and Fig. 5 .

The hydrocarbon signals in the T ₁ -T ₂ spectra obtained in Comparative Examples 1 to 3 all have peak shape superimposition, which can be used for qualitative analysis. For quantitative analysis, these signals have low signal-to-noise ratio, poor resolution, and inconsistent interpretation. low quality.

Example 3

This embodiment provides a coupling of the nuclear magnetic resonance instrument and parameters of the present invention to test the shale oil core samples Y-1 to Y-10 of Well Y, see Figure 7 and Figure 8, and the specific data analysis is as follows:

The parameters of the NMR instrument are: the magnetic field strength is 20Mhz, the pulse sequence is the inversion recovery method IR-CPMG, the echo interval TE is 0.06ms, the waiting time TW is 10ms, the inversion method is the regularization method, and the test is carried out.

Among them, Fig. 7 is the T ₁ -T ₂ spectrum obtained from the shale oil core sample Y-1. It can be seen that the signal-to-noise ratio of the spectrum is high, with 4 signal peaks, and the TOC signal peak is the same as the movable oil peak on the right. The signal peaks can be clearly separated by adjusting the amplitude contour.

Fig. 8 is the correlation analysis diagram of the percentage S _TOC of the T ₁ -T ₂ spectrum TOC signal peak obtained from shale oil core samples Y-1 to Y-10 and the TOC of the rock pyrolysis method. It can be seen that the correlation is very High, the correlation coefficient reached 0.96.

To sum up, the method of the present invention can identify the multi-components of source rock reservoirs through T ₁ -T ₂ two-dimensional nuclear magnetic resonance technology without sample processing, and further obtain high-quality T ₁ -T ₂ spectra to calculate The total organic carbon content (TOC) overcomes the uncertainty in the characterization of source rock kerogen and organic matter content caused by different instrument parameters and different measurement parameters, and realizes high-precision quantitative calculation of TOC content, so that it can be used in the evaluation of source rock reservoir oil content At the same time, the properties of source rocks are evaluated, which provides reliable technical support for the evaluation of source rock oil and source rock gas sweet spots.

Any reference to any numerical value in this invention includes all values in increments of one unit from the lowest value to the highest value if there is a separation of only two units between any lowest value and any highest value. For example, if it is stated that the amount of a component, or the value of a process variable such as temperature, pressure, time, etc., is 50-90, in this specification it means that 51-89, 52-88...and 69 Values such as -71 and 70-71. For non-integer values, 0.1, 0.01, 0.001 or 0.0001 may be considered as a unit as appropriate. These are just some specifically indicated examples. In the present application, in a similar manner, all possible combinations of values between the lowest value and the highest value enumerated are considered to have been disclosed.

It should be noted that the above-mentioned embodiments are only used to explain the present invention, and do not constitute any limitation to the present invention. The invention has been described with reference to typical embodiments, but the words which have been used therein are words of description and explanation rather than words of limitation. The present invention can be modified within the scope of the claims of the present invention as prescribed, and the present invention can be revised without departing from the scope and spirit of the present invention. Although the invention described therein refers to specific methods, materials and examples, it is not intended that the invention be limited to the specific examples disclosed therein, but rather, the invention extends to all other methods and applications having the same function.

Claims (7)

1. A method utilizing T ₁ -T ₂ two-dimensional nuclear magnetic resonance to evaluate source rock TOC, is characterized in that, comprises the following steps: Step 1: Establish a relationship model between the signal area percentage S _TOC representing TOC on the T ₁ -T ₂ spectrum of the source rock and the measured total organic carbon content TOC of the corresponding source rock; Step 2: Perform T ₁ -T ₂ two-dimensional nuclear magnetic resonance analysis on the source rock to be tested to obtain the T ₁ -T ₂ spectrum of the source rock to be tested; Step 3: Calculate the TOC of the source rock to be tested based on the relationship model obtained in Step 1. 2. the method for evaluating source rock TOC according to claim 1, is characterized in that, described step 1 comprises: Step 11: Perform T ₁ -T ₂ two-dimensional nuclear magnetic resonance analysis on the source rock to obtain the T ₁ -T ₂ spectrum of the source rock; Step 12: Use the rock pyrolysis method to actually measure the total organic carbon content of the source rock, and obtain the measured total organic carbon content TOC of the corresponding source rock; Step 13: Based on the T ₁ -T ₂ spectrum of the source rock obtained in step 11 and the measured total organic carbon content TOC of the corresponding source rock obtained in step 12, obtain the T ₁ -T ₂ spectrum characterization of the source rock The relationship model between the signal area percentage S _TOC of TOC and the measured total organic carbon content TOC of the corresponding source rock. 3. The method for evaluating source rock TOC according to claim 1 or 2, characterized in that, in step 11 and/or step 2, T ₁ -T ₂ two-dimensional nuclear magnetic resonance analysis magnetic field strength is 20 ± 5Mhz, the probe The caliber is not less than 15mm, the pulse sequence is the inversion recovery method IR-CPMG, the echo interval TE is 0.06ms, the waiting time TW is 10ms, and the inversion method is the regularization method. 4. The method for evaluating source rock TOC according to claim 1 or 2, characterized in that the T ₁ -T ₂ spectrum signal-to-noise ratio SNR>1000 measured in step 11 and/or step 2, the number of signal peaks Not less than 3. 5. the method for evaluating source rock TOC according to claim 1, is characterized in that, in described step 13, also comprises the following steps: Step 13a: Calculate or read the T ₁ -T ₂ spectral signal area A _TOC , Step 13b: Calculate or read the total effective area ΣA _i of the T ₁ -T ₂ spectrum, Step 13c: Calculate A _TOC as a percentage of ΣA _i S _TOC : S _TOC ＝(A _TOC /∑A _i )×100％ Formula 1 Step 13d: Establish a relationship model between S _TOC and TOC through linear regression: TOC＝a×S _TOC +b Formula 2 In the formula, a and b are the regression coefficients, where a is the slope of the regression line; b is the intercept of the regression line. 6. The method for evaluating source rock TOC according to claim 4, characterized in that, in the step 13b, the effective area does not include noise signals. 7. The method for evaluating source rock TOC according to any one of claims 1-6, characterized in that T ₁ ranges from [15,500]; T ₁ /T ₂ ranges from [30,600].

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